This invention relates generally to apparatus and methods for testing gelation of a substance and more particularly, but not by way of limitation, to pressure and temperature controlled pressure pulse gelation test apparatus and methods.
The drilling and completing of oil or gas wells requires the use of various types of blended substances, some of which need to cure, gel or polymerize over time to be properly useful once they are placed in the well (the term "gel" and its formatives will be used herein as the generic term encompassing the phenomena for which the present invention is used). For example, sealants comprising silicate solutions are blended and flowed into a well for sealing water zones.
Because blended substances such as the exemplary sealant experience a transition in fluid characteristics in the gelling process and because such transition affects the ability of the substance to be pumped into the formation, it is important to know the gelling time characteristics of the compositions, in general, and of specific batches of a composition, in particular. It is also important to know the gel strength characteristic of a substance once it has gelled so that one will know which substance to use for a particular strength requirement. Such characteristics need to be determined with reference to selectable temperatures and pressures which correspond to those that will likely affect the substance in the actual environment in which it is to be used. Therefore, there is the general need for an apparatus and method for testing these gelation characteristics of a substance.
An accurate method for measuring the onset or initiation of gelation of a substance at selectable temperatures and pressures has been a problem because prior techniques have been too subjective or labor-intensive or they have degraded the tested substance when it is of a type having a weak initial gel structure. An example of the former shortcoming is found in columns 5 and 6 of U.S. Pat. No. Re. 30,767. Another example is that of the visual means of detection heretofore used. In this visual means, the solution or blend to be tested is prepared and placed in a glass bottle. By periodically tilting the bottle, one can easily observe if the sample is still fluid or if it has gelled. This technique is limited to lower temperature environments. For higher temperature tests, an oil bath with a water based test sample is placed in a glass pressure bottle. This method is unsafe for general usage because at a temperature of 250.degree. F., for example, the pressure in the bottle could be sufficiently great (e.g., 30 psi) to create a high risk of injury from flying glass and from the reaction between the superheated water and oil if the pressure bottle ever exploded while it is being manually inspected.
Prior techniques which degrade a substance having a weak initial gel structure, and thus techniques which would yield inaccurate results as to such a substance, are devices referred to as viscometers or consistometers or thickening time/gel strength testers utilizing paddle/container combinations exhibiting relative movement between the paddle and container. Although the relative movement between these components can be very slow, it still exerts a sufficient mechanical action to degrade weak gel structures.
Therefore, there is the need for an improved apparatus and method for testing gelation, such as gel transition time and gel strength phenomena, in samples of substances having even relatively weak gel forming structures. Such an apparatus and method should be designed for making such tests under controllable temperature and pressure conditions, such as the high temperatures and pressure which will be encountered in a well. Such an improved apparatus and method should also be relatively easy and safe to use.